1. Field of the Invention
The present invention provides an improvement for use in a catheter system having a work element coupled to a drive shaft disposed within a flexible tubular catheter body. More particularly, the present invention provides an improved tracking tip to facilitate movement of the work element within the catheter body and to minimize the risk of the work element puncturing the wall of the catheter body.
2. Description of the Background Art
Arteriosclerosis, also known as atherosclerosis, is a common human ailment arising from the deposition of fatty-like substances, referred to as atheromas or plaque, on the walls of blood vessels. Such deposits occur in both the peripheral blood vessels, which feed the limbs of the body, and the coronary vessels, which feed the heart. When deposits accumulate in localized regions of a blood vessel, stenosis, or narrowing of the vascular channel, occurs. Blood flow is restricted and the person's health is at serious risk.
Numerous approaches for reducing and removing such vascular deposits are known, including balloon angioplasty, in which a balloon-tipped catheter is used to dilate a region of atheroma; atherectomy, in which a blade or cutting bit is used to sever and remove the atheroma; spark gap reduction, in which an electrical spark burns through the plaque; and laser angioplasty, in which laser energy is used to ablate at least a portion of the atheroma. In order to facilitate treatment of the stenosis, it is often desirable to obtain a visual image of the interior of the blood vessel within the region of interest. Catheters having imaging elements such as ultrasonic transducers are often used to obtain these images.
In many cases, catheter systems having imaging or interventional devices will include a rotatable drive shaft disposed within the flexible catheter body. Catheters of this type will have some type of work element fixed to the distal end of the drive shaft. In imaging systems, the work element is typically an ultrasonic transducer or a movable mirror associated with an ultrasonic transducer.
An exemplary catheter system having a rotating ultrasonic transducer coupled to a drive shaft is disclosed in U.S. Pat. No. 4,794,931, the disclosure of which is incorporated herein by reference. In this system, a drive shaft disposed within a flexible tubular catheter body is used to rotate an ultrasonic transducer about an axis parallel to the catheter body. The ultrasonic transducer is thereby caused to scan a region of the blood vessel in a plane normal to the catheter body.
Another catheter system, which may include an imaging or interventional work element connected to a rotating drive shaft, is disclosed in U.S. Patent application Ser. No. 07/975,769, filed on Nov. 13, 1992, the disclosure of which is incorporated herein by reference. This "common lumen" catheter system includes a proximal region having multiple lumens for carrying a guidewire and various work elements and a reduced profile single lumen distal region. A catheter system of this type is advantageous in that the common lumen distal region, having a narrower profile, is able to enter into more constricted areas than would otherwise be possible.
A catheter of the type having a common distal lumen is used as follows. First, a guidewire is advanced into the patient until it lies within a region of interest, typically a region of stenosis within the blood vessel. After the guidewire is positioned, the proximal end of the guidewire is fed into the distal tip of the common lumen and the catheter is advanced into the patient over the guidewire. As the catheter advances into the patient, the guidewire enters and travels through a selected lumen of the multiple lumen proximal region of the catheter body.
Advancement of the catheter into the patient continues until the common lumen distal region lies within the blood vessel in the region of interest. The guidewire is then withdrawn into the proximal region to clear the common lumen. A suitable work element, often a rotating ultrasonic transducer, may then be advanced through the common lumen into the region of interest. Use of a catheter system of this type is described more fully in U.S. Patent application Ser. No. 07/975,769.
It is generally desirable to make the diameter of a catheter body as small as possible to allow the catheter to enter narrow and tortuous regions of the patient's vascular system. As the catheter body size is minimized, the thickness of the catheter wall is decreased and the danger that the wall will rupture may become significant.
While the danger of catheter wall failure is present in any catheter system, it may be particularly troublesome in a common lumen catheter of the type described in application Ser. No. 07/975,769. First, the common lumen is designed specifically to be small in diameter and to be positioned in particularly narrow and twisted regions of the vascular system. Second, the work element in a common lumen catheter not only rotates but also advances lengthwise through the lumen. When the rotating work element encounters a kink in the catheter body, it will impact the wall at the kink and in some cases may cause failure of the catheter body wall.
For these reasons, it would be desirable to provide an attachment for a work element that would allow the work element to track the lumen of the catheter body more reliably with less danger of puncturing the catheter wall. Such an improved tracking tip could find use in any catheter system having a work element and a tubular catheter body. It is expected, however, that such an improved tracking tip will prove particularly advantageous in a catheter system such as that described in application Ser. No. 07/975,769, where the work element is rotating, where it may be advanced longitudinally through the catheter body, and where the catheter body is particularly small in diameter.